The invention concerns a device for transferring a paper web from the press section to the drying section of a paper machine.
Most modern paper machines use rope carriers for "threading" the paper web, such as after a standstill or web break, into the drying section of the peper machine. The drying section normally consists of several drying cylinder groups, each group having several drying cylinders. These rope carriers are designed as set out below. In each drying cylinder group, two ropes run along the path of the paper web. To start the transfer operation one introduces a narrow edge strip of the paper web, the so-called transfer strip, in the drying cylinder group. At the end of the drying cylinder group, the transfer strip is passed to the next drying cylinder group.
During this threading phase, the remaining part of the paper web is passed from the screen or from one of the press rolls to a scrap collection container. Next, the transfer strip is widened until it reaches the full width of the web so that, lastly, the entire paper web is passing through the drying section.
As commonly known, the rope carrier is located on the tending aisle edge of the drying cylinders so as to be outside the paper web width. Therefore, the transfer strip must be diverted sideways from its normal path before the point at which the transfer strip enters the rope carrier. A prior rope carrier has been described in the German Patent Publication No. 1,022,900 (to which U.S. Pat. No. 2,716,291 is a counterpart). Two ropes are always used which form a rope carrier since the leading end of the transfer strip is pinched between the two ropes.
Another previously known arrangement (such as in German Patent Publication No. 23 65 438 which is similar to U.S. Pat. No. 4,000,035), is a so-called contact felt group. The contact felt group uses a narrow guide belt instead of a pair of ropes. This belt can proceed through a drying cylinder group on two different courses. It runs either in an ineffective position alongside and outside the paper web width, as during the normal production operation, or it runs at the edge of the paper web and within its width. The latter position is assumed, for instance, with the aid of laterally shiftable pulleys, when a threading operation is to take place. The belt carrier can thus thread the transfer strip into the drying cylinder group within the paper web width, and it is not necessary to divert the transfer strip leader sideways as in the case of the rope carrier. The transfer strip rather runs from the outside in its normal position between the belt carrier and the drying felt or drying screen. Upon completed threading, the belt carrier must be moved sideways out of the paper web area into its ineffective position. The belt carrier runs now on the outer edge of the drying cylinder. For the next transfer operation it must be moved again into the area of the paper web.
In the belt carrier described above, a single rope acting in the same fashion as the belt could be used as well instead of it. The term "guide belt" comprises hereafter also a single rope, and whereas the term "rope" is always part of a rope carrier featuring a pair of ropes.
The prior devices have proved themselves. But sometimes it is disadvantages that the belt carrier and/or rope carrier must during the entire operating time of the paper machine continually revolve at the speed of rotation of the drying cylinders. Attempts have already been made at eliminating this disadvantage by providing on each drying cylinder a loose rim for the belt and/or the rope pair (see German Patent Publication No. 1,002,900). Such rims also provide for different speeds between the drying cylinders and the belt and/or the ropes. But the design expense for loose rims is extremely high. In addition, they must be serviced in regular intervals.